Vehicles today use, for example, urea as reducing agent in SCR (selective catalytic reduction) systems which comprise an SCR catalyst in which said reducing agent and NOx gas can react and be converted to nitrogen gas and water. Various types of reducing agents may be used in SCR systems. AdBlue is an example of a commonly used reducing agent.
One type of SCR system comprises a container which holds a reducing agent. The system has also a pump adapted to drawing said reducing agent from the container via a suction hose and supplying it via a pressure hose to a dosing unit situated adjacent to an exhaust system of the vehicle. The dosing unit is adapted to injecting a necessary amount of reducing agent into the exhaust pipe upstream of the SCR catalyst according to operating routines which are stored in a control unit of the vehicle. To make it easier to regulate the pressure when there are small or no dosing amounts, the system comprises also a return hose which runs back to the container from a pressure side of the system.
It is of utmost importance that the reducing agent comprises a desired and expected content of an effective component, such as urea. In another case, a supply of said reducing agent will be inappropriate leading to inadequate emission control. Today there is a risk of mistakenly providing other liquids to said container for said reducing agent. Also, even intended provision of an undesired liquid to said container may be performed in case of tampering. There is also a risk that a provided reducing agent simply does not meet the specification of its content, which will render an unwanted concentration of said effective component.
US20080173074 relates to a method for measuring a prevailing concentration of urea in a container based upon determined values of resistance.